Lesson 60 Introducing Transformers and Putting It All Together

Chapter Lesson 60 Introducing Transformers and Putting It All Together

Electronic Circuits for the Evil Genius Second Edition 64 Lessons with Projects
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Electronic Circuits for the Evil Genius Second Edition 64 Lessons with Projects

  • 242Section 17 ■Applying the Op Amp: Building the Intercomyou will need to do some measuring at theoutput, and don’t want the speaker to get inthe way.4.Scoping the circuit output.a. Replace the speaker with the connectorcord clips, the red clip to C3 (neg), andblack to ground. The cord is plugged intothe sound card “line in,” or microphoneinput.b. With the volume turned all the way down,whistle and look at the signal on the scope.c. It should be identical to the signal takendirectly from the speaker earlier.d. Now turn the volume all the way up.Whistle again. Draw this on the scope facein Figure L59-5.5.Check out the AC voltage of the maximumoutput of your whistling using the DMM.______Vac Max.6.Listen to the circuit output.a. Now before you put the output speakerback in, solder the ends of the dual-wireline to your speaker. That line should be atleast five feet long. Place it back into thecircuit.b. Place the input and output speakers as farfrom each other as possible.c. Whistle into the input speaker.Hmm. The output is very quiet, even atfull volume.The last component will take care of that.Lesson 60Introducing Transformers and Putting It All TogetherSo you’ve seen that speakers aren’t microphones.The small signals they produce need a differentkind of preamp to get a clean signal from thissubsystem to the next stage of the amplifiersystem. Right now, the output directly from thespeaker is a paltry 1 millivolt. So the output fromthe amplifier is also very weak. Such a smallsignal needs to be cleanly amplified even before itis fed to the preamp. To restate, the signal needs tobe preamplified before it gets to the preamplifier.Without having a two-stage preamplifier, there just isn’t enough signal there to control the power amplifier.Here I will introduce transformers as a methodto preamplify the signal to the preamp. It isfrequently done with microphones as well.Here is a great place to use a transformer. SeeFigure L60-1.Figure L59-5Figure L60-1